Portable handheld work apparatus, which are driven by an internal combustion engine, have a radial fan for cooling the engine in known embodiments. Such work apparatus include chain saws, brushcutters, suction and blower apparatus or the like. The radial fan arrangement includes a fan wheel and a spirally-shaped fan housing which at least partially encloses the fan wheel. The fan wheel is attached to the crankshaft of the engine and rotates with the crankshaft at the same rpm.
U.S. Pat. No. 4,716,860 discloses a fan arrangement wherein a take-out opening is provided in the region of the moved air flow for diverting a combustion air flow for the engine. The combustion air flow is branched off of the air flow moved by the fan arrangement. The take-out opening is disposed in such a manner that, because of the centrifugal force, the dirt particles are moved with the air flow component which is used as the cooling air flow component for the engine and that the air flow component, which is supplied to the carburetor, is substantially freed of the dirt particles.
To increase the power of internal combustion engines in portable handheld work apparatus, it has already been suggested to increase the air pressure of the combustion air flow. Here, the back pressure of the cooling air flow is used in order to supply the branched-off combustion air flow with overpressure through a combustion air channel to the carburetor. Dirt particles are supplied with the inducted air flow during operation of a drive in a work apparatus under corresponding ambient conditions. These dirt particles are transported within the cooling fan assembly together with the air flow which is to be moved.
Various embodiments of preseparators are known which function to keep the entrained particles away from the take-out opening for the combustion air flow. The effect of such preseparators is dependent upon the position and the flow conditions and is therefore not always satisfactory. For insufficient separation, a high load is imposed on the air filter mounted upstream of the carburetor and has the consequence that frequent cleanings are needed or corresponding filter exchanges are made.